1. Field of the Invention
This application relates generally to drilling systems and methods.
2. Background Technology
Exploration drilling often includes retrieving a sample from a formation. The retrieved sample may then be evaluated to determine its contents.
In a wireline exploration drilling process, a drill string may be used to retrieve a sample from a formation. The drill string may include an open-faced drill bit, an outer tube of a core barrel assembly, and a series of connected drill rods, which may be assembled section-by-section as the drill bit and the core barrel assembly move deeper into the formation. The outer tube of the core barrel assembly may be connected to the drill bit and the series of drill rods. The core barrel assembly may also include an inner tube assembly, which may be releasably locked to the outer tube. With the inner tube assembly locked to the outer tube, the drill bit, the core barrel assembly and the drill rods may be rotated and/or pushed into the formation to allow a core sample to be collected within the inner tube assembly. After the core sample is collected, the inner tube assembly may be unlocked from the outer tube. The inner tube assembly may then be retrieved using a retrieval system, while portions of the drill string remain within the borehole. The core sample may be removed from the retrieved inner tube assembly, and after the core sample is removed, the inner tube assembly may be sent back and locked to the outer tube. With the inner tube assembly once again locked to the outer tube, the drill bit, the core barrel assembly and the drill rods may again be rotated and/or pushed further into the formation to allow another core sample to be collected within the inner tube assembly. Desirably, the inner tube assembly may be repeatedly retrieved and sent back in this manner to obtain several core samples, while portions of the drill string remain within the borehole. This may advantageously reduce the time necessary to obtain core samples because the drill string need not be tripped out of the borehole for each core sample.
The inner tube assembly may include a core lifter. The core lifter may be used to grip the core sample to facilitate its retrieval. Over time, the core lifter may wear down, which can cause damage that prevents it from gripping the core sample. This damage can prevent retrieval of the core sample.